Acrylic artificial marbles obtained by blending an acrylic resin with inorganic fillers such as aluminium hydroxide and the like have various prominent functions and characteristics such as an excellent appearance, soft feeling, weatherability and the like, and are widely used for counters such as a kitchen counter and the like, lavatory dressing tables, waterproof pans and other building uses. These artificial marbles are generally produced by filling a mold with what is called slurry obtained by dispersing inorganic fillers in acrylic syrup, and by curing and polymerizing the filled slurry at relatively low temperature. However, since this acrylic syrup has a low boiling temperature, there is no other selection than lowering the curing temperature, and consequently a long time is required for molding leading to low productivity. Further, since there is a problem regarding the filling ability of the slurry into a mold, the configuration of the resulting molded article is limited.
To improve these defects, there have been conventionally made investigations to produce an acrylic artificial marble by heat and pressure-molding of a premix obtained by thickening resin syrup with a thickening agent.
For example, Japanese Patent Application Laid-Open (JP-A) No. 5(1993)-32720 discloses an acrylic premix for an artificial marble, excellent in handling property and molding property, prepared by blending acrylic syrup with a crosslinked resin powder having a specific degree of swelling obtained by suspension polymerization. Further, Japanese Patent Application Laid-Open (JP-A) No. 6(1994)-298883 discloses an acrylic premix for an artificial marble, excellent in low shrinking property in heat-curing, prepared by blending acrylic syrup with a thermoplastic acrylic resin powder which is poor-soluble in the syrup. Further, Japanese Patent Application Laid-Open (JP-A) No. 6(1994)-313019 discloses an acrylic premix for an artificial marble which prevents cracking in molding and provides improved appearance and thickening stability of the resulting molded article by blending acrylic syrup with a resin powder prepared by the spray drying-treatment of a crosslinked polymer obtained by emulsion polymerization.
However, when the resin powders disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 5(1993)-32720 and 6(1994)-298883 are used, there are problems that production cost increases since a large amount of resin powder is required for thickening acrylic syrup and, further, productivity lowers since a long time is required for thickening.
Further, when the resin powder disclosed in Japanese Patent Application Laid-Open (JP-A) No. 6(1994)-313019 is used, there is a problem that aging of the premix for a long time (approximately 24 hours) is necessary for thickening up to such level that enables heat and pressure-molding.